Chronographing Results

Discussion in 'Range Reports' started by old, Dec 24, 2015.

  1. old

    old New Member

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    Reloads, 125gr RNFP, 5.3gr HP-38, Chrony (F1, I think, from memory?)

    Am interested in knowing if muzzle velocity variations are normal?

    Fired following 357 mag revolvers, 12 rounds each:

    Ruger, sp101-2, velocity variations: 864.2 to 963.4 fps
    Ruger, sp101-3, 940.4 to 1014 fps
    Ruger, Security 6, 4 inch barrel, 981.3 to 1040 fps

    Was firing from seated position, using sandbags as a rest, approx 5 yds from chronograph. I'm thinking lack of a fixed shooting rest may be cause of inconsistencies?

    Comments please. ................ old
     
    Last edited: Dec 24, 2015
  2. gunslinger669

    gunslinger669 Active Member

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    The combinations of shooting off of sandbags and not a fixed rest as well as powder distribution within the casings can cause some deviation, but yours appears to be larger than I would expect. What was the weather and what was the distance of the chronograph from the muzzle?
     

  3. old

    old New Member

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    Approx 5 yds from muzzle to chrono. Did not think about that until later. Chrono manual says minimum is 10 feet. Day was sunny, 60 deg F, was under shade trees, so did not install light shields on chrono.

    Had not thought about powder distribution. Will pay closer attention to that next time. The good news is I live on a farm, have my own shooting range, so repeat chrono-ing is easy. :D
     
  4. gunslinger669

    gunslinger669 Active Member

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    The angle of the trajectory is important as well- repeatable consistency is key. Weigh your powder for each round to the 100th of a grain ( 5.3?). Tape measure the chronograph to the muzzle plane. Settle the powder for each round just before you pull the trigger.

    Do you have a consistent OAL and crimp?
     
  5. phideaux

    phideaux Well-Known Member Lifetime Supporter

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    Different barrel lengths..?

    Hmmmmmm.




    Jim
     
  6. gunslinger669

    gunslinger669 Active Member

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    Yes, between the three revolvers, but I believe he's asking about the wide range of results for each individually, not between each revolver.
     
  7. phideaux

    phideaux Well-Known Member Lifetime Supporter

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    Yeah, I think your right.

    But I usually always see some variation, then, my chrony gives deviations and averages.

    Never really thought too much of it, but 100fps variation ,with EXACT same loads (bullet, powder, brass, primers) don't seem right.

    sumpin aint kosher..;)



    Jim
     
  8. old

    old New Member

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    Yup!

    You guys got it right. I was not clear with the original question. I understand why muzzle velocities vary with barrel length. I was more concerned with why so much variation between high and low on a given revolver.

    Got some good ideas from your posts. Will have at it again as weather permits. No problems with OAL or crimps being consistent.

    Hope Santa leaves y'all diamonds instead of coal (like I'll get).

    old ........... :D
     
  9. gunslinger669

    gunslinger669 Active Member

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    Screw diamonds, gimme guns and ammo!

    Merry Christmas all!
     
  10. RFF

    RFF Member

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    From my experience with Chronographs, I always use the sunshades for accuracy.